Mailbox
A mailbox was a receptacle for letters and packages that were to be sent through the mail.
In 2004, a United States Postal Service mailbox was present on the streets of Detroit. (ENT: "Carpenter Street")
At the dormitory at the Noonien-Singh Institute for Cultural Advancement, there was a drawing of a house with a cow and a rabbit and a mailbox out front. This drawing was on a piece of paper that was hanging on the wall. This drawing was near the dorm room of Khan Noonien Singh, who most likely drew it. (SNW: "Tomorrow and Tomorrow and Tomorrow")
In the 23rd century, the Iotians of Sigma Iotia II had green mail boxes on their streets of their settlements. (TOS: "A Piece of the Action")
When Bradward Boimler was clinically dead, he dreamed he was on James T. Kirk's ranch in Idaho, where he met Hikaru Sulu, who was taking care of his horse named Atlas while Kirk was away "travelling through time" or something like that. Boimler had expected Kirk to be there, due partially to the US Mail box (presumably with Kirk's name on it). (LD: "Crisis Point 2: Paradoxus")